Two-stroke combustion engines are extensively used in a variety of handheld tools such as, but not limited to, chainsaws, hedge trimmers, grass trimmers, blowers and mowers. When a two-stroke combustion engine is subjected to a very small load during operation, the engine speed may reach a very high value. This results in premature wear and failure of the engine. Hence, there is a requirement to regulate the engine speed in order to avoid any damage to the engine.
Typically, ignition timing of the engine relative to a top dead center (TDC) position is adjusted to regulate the engine speed. It is well known in the art, in case the engine speed reaches a predetermined threshold engine speed, the engine speed is regulated by gradually and continuously retarding the ignition timing relative to the TDC position. The ignition timing relative to the TDC refers to an angular position of the crankshaft in terms of the number of degrees before the TDC position at which a spark ignites the air-fuel mixture in a cylinder during compression stroke. However, by decreasing the ignition timing to very close to the TDC, blow out of unburned fuel in the exhaust muffler may occur. This results in a loss of power output, increased pollutants in the exhaust gases and unwanted noise. Moreover, the temperature of the exhaust gases is very high and this may also leads to unintended glow ignition.
Further, the ignition timing is also dependent on the engine temperature; in case of a cold engine decreasing the ignition timing to very close to the TDC results in incomplete combustion and increases pollutants in the exhaust gases.
In some cases, along with the control of the ignition timing, cut-out is employed to regulate the engine speed. During cut-out, ignition is skipped for some revolutions of the crankshaft. This helps in regulating the engine speed and also decreases the temperature of the exhaust gases. However, it has the disadvantage of blowing out unburned gases during the engine revolutions for which ignition is skipped and results in an increased amount of pollutants in the exhaust gases. Further, cut-out also affects the operation due to an uneven power output by the engine.
In light of the foregoing, there is a need for an improved system and method for regulating the speed of a two-stroke combustion engine. Moreover, there is a need for a means for regulating the engine speed to provide improved engine performance and efficiency.